Anaerobic treatment of olive mill wastewater with digested piggery effluent

Anaerobic digestion of olive mill wastewater (OMW) in admixture with anaerobically digested piggery effluent (ADPE) was investigated. Successive volumetric increases of OMW ranging from 8 to 91% were mixed with ADPE and treated through an upflow anaerobic filter to promote gradual adaptation of the microbial consortium. The response of the digester was positive, and only at 91% v/v OMW was lower reactor performance obtained, suggesting that a concentration on the order of 83% v/v was the highest in terms of the efficiency and stability of the reactor. At this inlet composition, the mixture loading rate varied from 5.0 to 5.7 kg chemical oxygen demand$({\rm COD})/{\rm m}^{3}\cdot {\rm d}$and the total COD removal was 73 to 75%, with a gas production of 1.7 to 2.1${\rm m}^{3}/{\rm m}^{3}\cdot {\rm d}$(66 to 68%${\rm CH}_{4}$). The corresponding volume of ADPE (17%) was enough to maintain an influent ammonium-nitrogen$({\rm NH}_{4}{}^{+}\text{-}{\rm N})$concentration of 0.17 to 0.19 kg${\rm NH}_{4}{}^{+}\text{-}{\rm N}/{\rm m}^{3}$, which was practically spent.